1. Field of the Invention
The present invention relates to a read head with sunken prefill insulation for preventing lead to shield shorts and maintaining planarization and, more particularly, to first and second prefill insulation layers which are located in first and second recesses in a first shield layer on each side of a read sensor.
2. Description of the Related Art
The heart of a computer is an assembly is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Magnetic heads are constructed in rows and columns on a wafer by sputter deposition of various material layers and photolithography steps for masking the layers and forming them into desired shapes. In the formation of the read head portion of the magnetic head assembly a first shield layer and a first read gap layer are deposited on the wafer followed by deposition of multiple layers of the read sensor. A bilayer photoresist is then formed to cover all of the MR sensor material layer except for first and second openings located at first and second sites for first and second hard bias and lead layers which are to be connected to first and second edges of the MR sensor. Ion milling is then implemented to remove the sensor material within the first and second openings all the way down to the first read gap layer with a slight overmill of the first read gap layer to ensure that all of the sensor material has been removed. Hard bias material and lead layer material is then sputter deposited after which the bilayer photoresist is removed leaving first and second hard bias and lead layers connected to first and second side edges of a partially completed sensor. These series of steps define the track width of the read head which directly relates to the storage capacity of the rotating magnetic disk which will be discussed in more detail hereinafter.
Next, a bilayer photoresist mask is formed to cover the first and second hard bias and lead layers just deposited as well as the sensor with a back edge of the photoresist defining a location for the back edge of the MR sensor. Ion milling is again implemented which removes all of the sensor material except for the partially completed sensor which now has a defined front and back edge. A second read gap layer and a second shield layer are then formed followed by various sputter deposition steps and photolithography to form the write head. The wafer is then diced into rows of magnetic head assemblies after which each row is lapped to form the air bearing surface (ABS) of each magnetic head in the row. The row of magnetic heads is then diced into individual magnetic head assemblies for mounting on the aforementioned suspension and placement in a magnetic disk drive.
The storage capability of the magnetic disk depends, in part, upon the areal density of the read head which is a product of the track width density and the linear density of the read head. The track width density is expressed as tracks per inch (TPI) along the width of the magnetic disk and linear density is expressed as bits per inch (BPI) along the track of the magnetic disk. There is a strong-felt need to decrease the track width of the read head in order to increase the storage capacity of the. magnetic disk, which can be expressed as gigabits per square inch. For a one gigabit per square inch capacity the track width of the read head should be 0.75 to 0.80 xcexcm, for a 40 gigabit per square inch capacity the track width of the read head should be 0.35 to 40 xcexcm and for a 100 gigabit per square inch capacity the track width of the read head should be 0.18 to 0.20 xcexcm. With a decreased track width it becomes more important to accurately define the location of the first and second hard bias and lead layers at their connection to the MR sensor, as well as forming sharper junctions at these connections. In order to accurately locate the lead to sensor junction with a sharp connection it is important that the first read gap layer be planarized across the wafer so that a light exposure step of the photoresist for patterning is accomplished without shadows which are caused by steps or high profiles of the first read gap layer near the lead to sensor junction sites.
The linear bit density of the read head is determined by the spacing between the first and second shield layers of the read head. This spacing is dependent upon the thicknesses of the first and second read gap layers as well as the thickness of the sensor. A typical thickness of the read sensor is about 400 xc3x85, a typical thickness of the hard bias layer is about 150 xc3x85 and a typical thickness of the lead layer is about 600 xc3x85. Accordingly, with a 400 xc3x85 thick sensor the first and second hard bias and lead layers will project 350 xc3x85 above a top surface of the read sensor on each side of the sensor assuming that the first read gap layer is planar. The higher profile of the first and second hard bias and lead layers on each side of the read sensor requires the second read gap layer be formed on first and second steps with a dip down on the sensor therebetween. When the second read gap layer is sputter deposited onto the wafer the thickness of the second read gap layer portions on the upwardly sloping surfaces of the steps will be less than the second read gap layer portions which are flat on each side of the steps. The thinner second read gap layer portions on the steps increase the risk of pin holes which cause a shorting between the lead layers and the second shield layer. In spite of these problems there is a strong-felt need to reduce the thicknesses of the first and second read gap layers so as to increase the linear bit density of the read head. For a 1 gigabit per square inch capacity a typical thickness of each of the first and second read gap layers is 500 to 600 xc3x85, for a 40 gigabit per square inch capacity a typical thickness of these layers is 150 xc3x85 and for a 100 gigabit per square inch capacity a typical thickness of these layers is 10 xc3x85. It should be noted that it is not practical to reduce the thickness of the first and second lead layers because such a reduction will increase a parasitic resistance of the lead layers which competes with the resistance of the sensor.
A prior art teaching for decreasing the thickness of the first read gap layer without the risk of shorts is set forth in commonly assigned U.S. Pat. No. 5,568,335 which is incorporated by reference herein. In this patent first and second prefill insulation layers are deposited on the first shield layer on each side of the MR sensor followed by formation of the first read gap layer. The first and second prefill layers provide extra insulation between the first and second hard bias and lead layers and the first shield layer so as to lower the risk of shorting between the first and second hard bias and lead layers and the first shield layer. However, because of the profile each of the first and second prefill insulation layers they must be kept at least 10 xcexcm away from the side wall sites of the read sensor so that the formation of the first and second hard bias and lead layers at their junctions to the first and second side edges of the MR sensor can be accurately constructed with the aforementioned photolithography step. If the first read gap layer is not planar for a distance on each side of the read sensor the bilayer photoresist employed, for forming the first and second hard bias and lead layers, will have poor coating uniformity when it is spun onto the wafer substrate. This will prevent sharp junctions of the first and second hard bias and lead layers with the first and second side edges of the read sensor as well as poorly defining the size of the read head. A further problem with the prior art prefill design is that the spacing of the prefill insulation layers, in the order of 10 xcexcm, from the side edges of the read sensor increases the risk of shorting between the first and second hard bias and lead layers and the first shield layer, since only the first read gap layer is located within these locations. As previously mentioned, the first read gap layer is slightly overmilled on each side of the read sensor which further thins the first read gap layer in these locations.
Accordingly, there is a strong-felt need to reduce the thicknesses of each of the first and second read gap layers for promoting linear bit read density without increasing the risk of shorts between the first and second hard bias and lead layers and the first and second shield layers.
I have provided first and second prefill insulation layers which can be located below the first read gap layer for increasing insulation between the first and second hard bias and lead layers and the first shield layer to minimize the risk of shorting without impacting the photolithography step which is employed for defining the first and second hard bias and lead layers and their junctions with the first and second side edges of the read sensor. This has been accomplished by providing first and second recesses in the first shield layer which receive the first and second prefill layers so that top surfaces of the prefill layers can be lowered to completely eliminate their profile or, optionally, partially eliminate their profile, as desired. In the invention the read sensor is located above an unmilled planar portion of the first shield layer and the first shield layer is ion milled on each side of the read sensor to form the first and second recesses. In a first embodiment of the invention, the first and second recesses are sufficiently deep so that the first and second prefill layers sputter deposited therein become planar with the planar portion of the first shield layer directly below the read sensor. Accordingly, when the first read gap layer is sputter deposited, the first read gap layer will be planar across the wafer. This then permits an optimized photolithography step in forming the first and second hard bias and lead layers and their junctions to the first and second side edges of the MR sensor without the aforementioned shadowing. The first and second prefill layers can now be fabricated much closer to the first and second side edges of the MR sensor so as to minimize shorting between the first and second hard bias and lead layers and the first shield layer.
It should be noted that in the first embodiment there has been no relief for the shorting problem of the second read gap layer as it extends over the first and second steps caused by the high profiles of the first and second hard bias and lead layers adjacent the read sensor. The invention, however, may be employed for partially eliminating this problem or completely eliminating this problem, as desired. In a second embodiment of the invention the first and second recesses in the first shield layer are deeper than the first and second recesses in the first embodiment so that the first and second prefill layers are recessed below the planar portion of the first shield layer. This then permits a portion of the first and second hard bias and lead layers to be recessed within the first and second recesses in the first shield layer so as to reduce the first and second steps caused by the first and second hard bias and lead layers above the read sensor. It should be understood, however, that the second embodiment will have some impact on the photolithography step which defines the first and second hard bias and lead layers and their junctions with the read sensor, since there is a down step on each side of the read sensor after sputter depositing the first read gap layer.
In a third embodiment the first and second recesses in the first shield layer are still deeper than the recesses in the second embodiment to the point where the first and second hard bias and lead layers are sufficiently recessed in the first and second recesses that the second read gap layer is substantially planar across the top of the first and second hard bias and lead layers and the read sensor. Since the second read gap layer is substantially flat and has not climbed any steps its thickness will be substantially uniform so that shorting between the first and second hard bias and lead layers to the second shield layer is minimized.
An object of the present invention is to provide first and second prefill insulation layers below the first read gap layer and on each side of the read sensor for minimizing risk of shorts between the first and second hard bias and lead layers and the first shield layer all the way to locations adjacent the first and second side edges of the read sensor without impacting a photolithography step for defining the first and second hard bias and lead layers and their junctions to first and second side edges of the read sensor.
Another object is to provide first and second prefill insulation layers below the first read gap layer which can be employed for reducing the thickness of the first read gap layer and/or the second read gap layer.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.